It probably depends on whether the legal requirements are relative or absolute, and I don't know which they are. If the law explicitly stated measures you must take, they're probably fine. If the requirements use some kind of relative phrasing like that they must take "reasonable measures" to prevent sexual harassment, having all of that data already available might shift some jurors perspective of what "reasonable measures" are.
I wouldn't expect a judge to instruct a jury to disregard it, even in the case of signal to noise. There's nothing that makes the evidence inadmissable afaik (not a lawyer, so I could very well be wrong). It would be up to the plaintiff to demonstrate that the company failed in their obligations, and up to the company to defend that what they did was adequate.
> And isn't that why investigative agencies seemingly stopped asking ISPs and legislatures to record everyone's search-engine queries and DNS lookups - simply because the amount of actionable, useful data is impossible to find until some-bad-thing already happened?
The use of that data is also very different. There are a small number of crimes where a DNS lookup or search query is a crime in and of itself. Probably none, without other evidence. At best, they're circumstantial evidence.
In the case of digital communications, there are a lot of civil crimes that can be contained entirely within the communications. Sexual harassment, unlawful trade practices, etc. Likewise, the NSA is probably far more interested in everyone's email and chat than they are DNS lookups and search queries.